Failed to start up concurrent users module

I have a scheduled task that runs php CLI every few minutes. It runs ok, but very often it fails leaving a taskeng.exe window with the message Failed to start up concurrent users module! (and nothing else) which never closes.

What does it mean, exactly? Does that message come from php or from Windows? Should I worry about it/try to fix it?

This is the task configuration:

  ...
  <Triggers>
    <TimeTrigger>
      <Repetition>
        <Interval>PT1M</Interval>
        <StopAtDurationEnd>false</StopAtDurationEnd>
      </Repetition>
      <StartBoundary>2016-06-11T20:23:05.5135319</StartBoundary>
      <Enabled>true</Enabled>
    </TimeTrigger>
  </Triggers>
  <Principals>
    <Principal id="Author">
      <UserId>...</UserId>
      <LogonType>InteractiveTokenOrPassword</LogonType>
      <RunLevel>HighestAvailable</RunLevel>
    </Principal>
  </Principals>
  <Settings>
    <DisallowStartIfOnBatteries>false</DisallowStartIfOnBatteries>
    <StopIfGoingOnBatteries>true</StopIfGoingOnBatteries>
    <IdleSettings>
      <StopOnIdleEnd>true</StopOnIdleEnd>
      <RestartOnIdle>false</RestartOnIdle>
    </IdleSettings>
    <Enabled>true</Enabled>
    <Hidden>true</Hidden>
    <RunOnlyIfIdle>false</RunOnlyIfIdle>
    <WakeToRun>false</WakeToRun>
    <ExecutionTimeLimit>PT0S</ExecutionTimeLimit>
    <Priority>7</Priority>
  </Settings>
  <Actions Context="Author">
    <Exec>
      <Command>C:\...\php.exe</Command>
      <Arguments>services.php service=mora ctl=check</Arguments>
      <WorkingDirectory>C:\...</WorkingDirectory>
    </Exec>
  </Actions>
</Task>

Server OS is Windows Server 2012 R2 (64). Php version is 5.4 non thread safe (32) with Zend Loader 3.3.